JP3398301B2 - Edge interpolation method and edge interpolation device for image forming apparatus - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an edge interpolation method and an edge interpolation device for an image forming apparatus provided with a recording head having a plurality of recording elements arranged in a line.

[0002]

2. Description of the Related Art Conventionally, an image forming apparatus, for example, an LED head in which LEDs (light emitting diodes) are arranged in a line as a recording element, a thermal head in which heat-generating low antibodies are arranged in a line as a recording element, or an ink is ejected as a recording element. In a printer using a line head such as an inkjet head having outlets arranged in a line, the resolution of the head, that is, in the case of an LED head, each LED element of the LED head is left at a spacing in the raster direction, while in the case of a thermal head By recording the dots of the same size on the recording medium while keeping the raster direction spacing of each heating resistor of the thermal head, and in the case of the inkjet head the spacing of each ink ejection nozzle of the inkjet head in the raster direction. A binary image was formed. In these printers, a character image is simply a binary image corresponding to the resolution of the head, and a photographic image is reproduced by pseudo gradation processing such as a systematic dither method or an error diffusion method. On the other hand, in recent years, some of these line printers are capable of expressing multi-valued image data in one pixel with several gradation levels.

[0003]

Although such a conventional printer has improved gradation, it has a problem in that resolution causes jaggedness, which is called a jaggy, in a shaded portion of a character or a line drawing. . Especially in the case of a line head having a low resolution, the occurrence of jaggies was remarkable. In a low-resolution line head, when interpolating a portion where jaggies occur with small pixels, a gap occurs between dots, which is contrary to the discrimination resolution of human visual characteristics. There was a problem that the image looked out of focus.

Therefore, for example, in an electrophotographic image forming apparatus using an LED head, the effect of controlling the light emission time of one pixel and superimposing the energy distribution of light on the photoconductor and the photoconductor itself. Due to this resolution, the dot density is apparently higher than the spacing between the LED elements, and the dot position is controlled to reduce the jaggedness of the shaded portion of the recorded image to improve the print quality. Such technology is called edge enhancement technology,
The distribution of peripheral pixels has some influence on the target pixel and gives a printing effect, which is often used in electrophotographic image forming apparatuses.

However, this method requires special hardware for smoothing, a special image code obtained there, and a driver and a drive waveform necessary for driving this with an LED, and further comprises a printing mechanism section. and Ageruko a significant effect by limiting or electrical limitations of the process in accordance with the speed of the engine unit that has been difficult.

However, in a line printer such as a line ink jet printer, in which each pixel functions independently and has a large independent factor that does not affect other pixels, a pulling effect between dots is obtained. However, there is a problem that a gap is generated between the dots.
Further, when a multi-gradation image is handled, if a pattern matching method is independently used for multi-valued image data of 1 pixel several bits, the number of patterns is extremely increased, which is difficult to realize on hardware. There was a problem.

Therefore, according to the invention described in claims 1 to 9, the edge portion of the image can be smoothly reproduced by utilizing the data structure of the multi-value gradation image without additionally creating special image data. Provided is an edge interpolation method for an image forming apparatus, which can obtain a sufficient smoothing effect without using high-resolution image data and without causing a decrease in recording speed.

The inventions according to claims 10 and 11 are
It is possible to smoothly reproduce the edge part of the image by utilizing the data structure of the multi-value gradation image without additionally creating special image data, and without using high-resolution image data, Provided is an edge interpolation device of an image forming apparatus capable of obtaining a sufficient smoothing effect without causing a decrease in recording speed.

[0009]

According to the present invention, a recording head in which a plurality of recording elements are arranged in a line is provided, and the size of recording dots by each recording element of the recording head is changed to a recording medium. In an image forming apparatus that forms a multi-gradation two-dimensional image , multi-valued image data before interpolation and interpolation
Without changing the size of the subsequent multi-valued image data,
The dot size of the target pixel is changed according to the surrounding conditions.
Then, there is an edge interpolation method for performing edge interpolation.

[0010]

[0011]

[0012]

[0013]

[0014]

[0015]

[0016]

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described with reference to the drawings. (First Embodiment) In this embodiment, a case will be described in which edge interpolation processing is performed by pattern matching processing.

As shown in FIG. 1, a plurality of ink ejections for ejecting cyan ink from the upstream side of the rotation are provided so as to face the rotary drum 2 which holds the recording medium 1 such as paper fixedly and rotates in the direction of the arrow in the figure. A cyan ink line inkjet head 3 having nozzles arranged in a line, a magenta ink line inkjet head 4 having a plurality of magenta ink discharging nozzles arranged in a line, and a plurality of yellow ink discharging nozzles A line inkjet head 5 for yellow ink arranged in a line and a line inkjet head 6 for black ink in which a plurality of ink discharge nozzles for discharging black ink are arranged in a line are arranged in parallel with each other. In addition,
The order of arrangement of the inkjet heads 3 to 6 is not limited to this.

FIG. 2 is a block diagram showing the hardware configuration. The printer body 11 comprises a printer engine 12 which constitutes a printing mechanism section and a printer controller 13 which drives and controls the printer engine 12. The printer controller 13 is a personal computer. And the like are connected to the driver 15 of the host computer 14 including the above.

The host computer 14 matches the image data with the I / F characteristics of the printer main body 11 and from the driver 15 in the host computer 14 to the printer main body 11.
Transfer code or raster data to. The printer controller 13 develops coded image data from the host computer 14, for example, a page description language such as PDL into a bit map, performs each image processing, and stores it in a page memory in the printer controller 13. . The printer engine 12 converts the image data of the bitmap sent from the printer controller 13 into a drive signal for the engine, and drives the line inkjet heads 3 to 6.

With the recent widespread use of networks, it is not necessary for the connection between the host computer 14 and the printer body 11 to have a one-to-one relationship as shown in FIG. May be in a relationship. In addition, the printer controller 13
The I / F between the printer engine 12 and the printer engine 12 basically depends on the printer architecture and is not standardized.

FIG. 3 is a block diagram showing an image processing unit in the printer controller 13, which is a color conversion processing unit 21,
The color conversion processor 21 includes a UCR processor 22, a pseudo gradation processor 23, and a smoothing processor 24. For example, a standard RGB signal is input to an 8-bit monitor for each color and the color conversion processor 21 reproduces a color reproduction color in a printer. Convert to CMY color.

Next, in the UCR processing unit 22, CM
The black component is extracted from the Y color, the subsequent CMY color is determined, and finally converted into the CMYK color. Next, in the pseudo gradation processing unit 23, the data of one pixel is compressed into data of about 2 to 4 bits for each color by multi-value dither processing or multi-value error diffusion processing for each color. Finally, in the smoothing processing section 24, the edge portion is interpolated for each color to suppress the line drawing jaggies.

FIG. 4 is a block diagram showing the construction of the printer engine 12, which is provided with a control section 31, which controls the cyan ink line inkjet head 3, the magenta ink line inkjet head 4, and the yellow section. The line inkjet head 5 for ink and the line inkjet head 6 for black ink are driven and controlled.

The control section 31 causes the ink jet heads 3 to 6 to move in a direction orthogonal to the direction in which the recording medium 1 moves at a predetermined speed and a predetermined timing, that is, the rotation axis of the rotary drum 2. A head moving device 32 for moving the recording medium 1 in a direction, a paper conveyance motor 32 for picking up the recording medium 1 from a paper tray and conveying it to the rotating drum 2, a drum motor 33 for rotating the rotating drum 2, and a conveyed recording. The paper fixing device 34 that winds and fixes the medium 1 around the rotary drum 2 is driven and controlled.

When printing, the printer engine 12 causes the control section 31 to drive the paper transport motor 32,
The drum motor 33 and the paper fixing device 34 are driven at a predetermined timing, and the image data of the bit map from the printer controller 13 is fetched by the control unit 31 to drive the head moving device 31 and the inkjet heads 3 to 6. To do.

The smoothing processing section 24 of the printer controller 13 constitutes an essential part of the present invention, and its function will be described, for example, when the number of gradations is 3 bits for each color and 8 gradations. First, the printer has three capabilities
When a bit image can be handled, the pseudo gradation processing unit 23 can obtain multi-value image data of 3 bits for each color. This shows that, as shown in (a) to (g) of FIG. 5, a variable dot size of 7 kinds for each color is used per pixel, and a total of 8 gradations including white can be reproduced within 1 pixel. There is.

The size of each recording dot of each gradation is
The size is adjusted in advance for each color so that the density has a linear characteristic. Further, the dot size of the maximum gradation value generally forms a circle that completely covers the square pixel of the pure resolution of the printer engine 12, but here the gradation reproducibility is improved. Since the priority is given to the size configuration of the emphasized dots, the maximum gradation dots are not always in the shape of covering the square pixels of the pure resolution of the printer engine 12. Then, the pixel data having a plurality of dot sizes per pixel is used as it is as the interpolation data after the smoothing processing.

In order to simplify the description, the image data for 8 gradations will be described as 0 (white), 7 (black), and 1 to 6 as intermediate gradation values. First, the principle of smoothing processing in a normal binary printer will be described. In the smoothing process in a binary printer, the application of pattern matching is generally the mainstream.

Pixels to be interpolated by smoothing have a method of changing the resolution itself such as normal mode-fine mode conversion or normal mode-super fine mode conversion, which is often performed in facsimiles, and electrophotographic printers. There is a method of increasing the resolution in a pseudo manner by controlling the main scanning direction or the sub-scanning direction by dividing pixels with a resolution higher than the regular resolution of the printer like the edge enhancement technology, but the basic principle of pattern matching itself is the same. Therefore, the image data after interpolation is converted into high-resolution data information from the original image data by interpolation.

Here, the pattern size of the pattern matching will be described as 3 × 3 size for simplicity. FIG. 6 shows a 3 × 3 size pattern block for pattern matching. In the drawing, e is a target pixel to be smoothed, and 8 pixels a to d and f to i are reference pixels.
Here, the horizontal direction corresponds to 3 pixels in the main scanning direction, and the vertical direction corresponds to 3 lines in the sub scanning direction.

In the binary smoothing process, the pixel of interest e
Then, it is determined whether or not the target pixel is to be interpolated based on the white / black appearance pattern of the eight reference pixels a to d and f to i, and the value of the target pixel is rewritten if it is necessary to interpolate. 7 and 8 show examples of patterns that require interpolation in a 3 × 3 matrix. FIG. 7 shows a pattern example in which a minute pixel is added to a target pixel, and FIG. 8 shows a pattern example in which a target pixel is minutely deleted.

The interpolation patterns of FIGS. 7 and 8 are used, and when the pattern of the input pixel group corresponding to this matrix matches this interpolation pattern, the pixel of interest is converted into an appropriate interpolation value. In this smoothing process, the relationship between the interpolation pattern and the interpolation value may be stored in the ROM or the like as a table memory, and the position information of each pixel may be input as an address to output the interpolation value.
It may be configured by a logical operation of a complete gate circuit,
Easy to achieve. However, in the binary smoothing processing, the information amount of the image data after the interpolation is basically larger than that of the original image data before the interpolation.

Next, a smoothing method for multivalued image data will be described. When pattern matching processing is used for multi-valued image data, simply calculating, when handling 1-pixel binary data, the number of pattern matching combinations in a matrix size of 3 × 3 is 2 ⁹ = 51.
There are two patterns. When this is an 8-value of 3 bits per pixel, there are 8 ⁹ = about 134 × 10 ⁶ patterns. Since there are such patterns with a matrix size of 3 × 3, if the pattern size is further increased in order to improve the smoothing accuracy, the processing by simple pattern matching becomes practically impossible.

Therefore, in the present embodiment, paying attention to the fact that the smoothing effect is small at the intermediate gradation value in view of the visual characteristics, the smoothing processing is not performed at the intermediate gradation value, and the smoothing processing is performed only on the solid density portion. By doing so, the required number of patterns is reduced and a sufficient effect is obtained.

Specifically, the pattern matching processing for each color is valid only when the pixel value of the multivalued target pixel is the primary solid image data (0 and 7) for each CMYK. This means that if the pixel of interest has an intermediate gradation value, the smoothing process is not performed and the through process is performed.
In the pattern matching processing for each color, the pixel values of the multivalued target pixel and the reference pixel are 1 for each CMYK.
It is valid only for the next solid image data (0 and 7). This means that if even one pixel contains a halftone value in the pattern matrix, the smoothing process is not performed and the through process is performed.

As a result, the number of patterns used for pattern matching can be greatly reduced. In particular, in the case where even one pixel includes an intermediate gradation value in the pattern matrix, the number of combinations of patterns is basically the same as that of binary smoothing in the method in which smoothing processing is not performed.
The smoothing process with values can be applied as it is.

Next, the interpolation value output by pattern matching will be described. This is because the size of the original image data before interpolation and the image data after interpolation does not change by using the structure of the multi-valued image data for gradation reproduction as it is, therefore, adding high-resolution image data, A sufficient smoothing effect can be obtained without adding a new memory and without lowering the recording speed.

A method for actually obtaining the interpolation value will be described with reference to FIG. FIG. 9 shows a left-down edge, and the original value of the pixel of interest is 0 (white). In this example, the diagonal line 41 is an ideal straight line in this pattern, and the area ratio of the portion where the straight line intersects the target pixel on the black pixel side, that is, the hatched portion in the drawing to the target pixel is the gradation of the image. The value is converted into the ratio of and the interpolated value is determined.
Although the method of obtaining the ideal straight line is not basically limited, in the example of FIG. 9, the total area of the black pixels below the pixel intersecting the diagonal line 41 and the virtual area occupied by the lower side from the ideal straight line. It is desirable to set the areas of the black regions to be equal.

In FIG. 9, since the hatched area occupies 35% of the area of the target pixel, INT (7 × 0.35 + 0.5) is normally used in a device such as a monitor capable of reproducing gradation by brightness modulation. 2 is determined as an interpolation value by = 2, but in an apparatus that reproduces gradation by area modulation, this dot size is a size prioritized for gradation reproduction. The dot size of each gradation is not linear. Therefore, the dot of the gradation having the area ratio closest to the area ratio diagonally hatched from the area of each gradation pixel obtained by measurement in advance is determined as the interpolation value.

The results are shown in FIG. In FIG. 10, the value of “3” is selected as the gradation value by the interpolation processing in the pattern of FIG. As shown in FIG. 10, there are gaps between pixels due to interpolation depending on the pattern. However, due to the recent increase in resolution of printer heads, devising of the head driving method, and ink bleeding into the paper. By the blur effect of the edge part due to the dot itself,
The spatial frequency of this gap is higher than the human visual discriminable range, and the image is recognized as a smooth image with smoothed edges due to the visual integration effect.

The resolution of the printer engine 12 is 3
In the case of a printer of about 00 dpi, it is better not to use the small dots for the low gradation part in the interpolation to obtain a better result. Although the smoothing process in the 3 × 3 matrix has been described above for simplification, the present invention is not limited to this, and it can be applied to a 5 × 5 pattern matrix or a matrix size larger than that in order to improve the smoothing accuracy. Of course.

Next, the edge interpolation processing when the line inkjet head is specified will be described. Again, the printer's reproducibility can handle 3-bit images, 7 variable dot sizes are used per pixel, and 8 including white.
The case where the gradation can be reproduced within one pixel will be described as an example.

The line ink jet head variably controls the ink ejection amount from the ink ejection nozzle to reproduce the gradation. In this case, in view of the physical characteristics of the line inkjet head and the ink itself, generally, the ejection speed tends to be faster when the ejection amount is large and slower when the ejection amount is small. An example of this ink ejection characteristic is shown in FIG. In FIG. 11, the horizontal axis represents the discharge volume and the vertical axis represents the discharge speed. Also, P1, P2
, P3, P4, P5, P6, and P7 indicate the first to seventh gradations, respectively.

FIG. 12 is a diagram showing the concept of ink flying from a single nozzle 51 having an ink jet head onto the recording paper 52. An ink droplet 53 ejected from the nozzle 51 is recorded at an initial velocity V0. It is ejected onto the paper 52. At this time, since the recording paper 52 is moving at the speed Vd in the sub-scanning direction until the ink 53 reaches the recording paper 52, the amount of displacement from the reference position 54 on the recording paper 52 due to the increase or decrease of the ejection speed. x changes.

For example, if the distance between the nozzle 51 and the recording paper 52 is L, the displacement amount x can be obtained by x = L × Vd / V0. This is because L and Vd are basically the same in any state during printing, so that if V0 is constant, the displacement amount x is always constant and matches the engine resolution pitch. However, since the speed V0 changes depending on the amount of ejected ink, the printing pitch of large dots and small dots deviates from the reference pitch of the engine resolution.

In FIG. 13, (a) and (c) show examples of printing in an ideal system when the ejection speed for each ink ejection amount is constant. That is, both the large dot D1 and the small dot D2 are printed at the ideal center position.
13A shows the case where the small dots D2 are printed before the large dots D1 with respect to the movement of the recording paper, and FIG. 13C shows the small dots D2 with the movement of the recording paper. Shows a case in which printing is performed after the dot D1 having a large dot.

However, in reality, the arrival of small dots on the recording paper is delayed compared to the large dots.
The ideal system of (a) of 3 becomes as shown in (b) of FIG. 13, and the ideal system of (c) of FIG. 13 becomes as shown in (d) of FIG. That is, in FIG. 13B, the small dot D2 is displaced in the direction opposite to the moving direction of the recording paper and is printed close to the large dot D1 to be printed later. Also, in FIG. 13 (d), a small dot D
2 is displaced on the side opposite to the moving direction of the recording paper, and is printed away from the previously printed large dot D1.

Smaller dot D2 than larger dot D1
In the case of (b) of FIG.
2 shifts in the direction of narrowing the interval between dots, which is a good smoothing effect, but large dot D1
In the case of (d) of FIG. 13 in which the smaller dot D2 is printed later, the smaller dot D2 is displaced in the direction of widening the interval between the dots, which adversely affects the smoothing effect.

Therefore, when a dot D2 smaller than the large dot D1 is printed later, that is, when an edge on the rear side with respect to the sub-scanning direction in which the recording paper moves is interpolated with a small dot, (e) of FIG. As shown in, the edge interpolation is performed by using the dot D3 having a size several steps larger than the originally used dot size. As a result, it is possible to prevent the intervals between the dots from being opened and to enhance the smoothing effect.

(Second Embodiment) In this embodiment, a case will be described in which an edge interpolation process is performed by applying a filtering process. As shown in FIG. 14, a 3 × 3 matrix extracting unit 61 including a flip-flop circuit group for fetching the image data of the preceding one line, the present one line, and the following one line is provided, and this matrix extracting unit 61 is required for filtering processing. 3 × 3 pixels centering on the target pixel * are extracted.

The 3 × 3 pixel information extracted by the 3 × 3 matrix extracting unit 61 is supplied to the edge detection filtering unit 62, the isolated point detection filtering unit 63 and the smoothing filtering unit 64, and also to the delay circuit 65. We are supplying.

The edge detection filtering unit 62 is
The edge detection filter having the structure shown in FIG. 15A is used, and the extracted 3 × 3 pixel information is filtered by this edge detection filter. The edge detection filter is configured not to detect horizontal lines and vertical lines because detection of horizontal lines and vertical lines is likely to cause blurring in a character / line image at an intermediate gradation value. Then, by comparing the result of the filtering process with the threshold value Th1 in the threshold value determination unit 66, it is determined whether or not the pixel of interest * is the edge portion.

The isolated point detection filtering unit 63 is
The isolated point detection filter having the configuration shown in FIG. 15B is used, and the extracted 3 × 3 pixel information is filtered by the isolated point detection filter. In the isolated point detection filter, the edge detection filter shows a very strong reaction to an isolated point in addition to the edge part of a character or a line, and therefore a filter showing a higher value at the isolated point detection than at the edge detection. Are using. Then, by comparing the result of the filtering process with the threshold value Th2 in the threshold value determination unit 67, it is determined whether or not the pixel of interest * is an isolated point.

The smoothing filtering unit 64 is shown in FIG.
Using a smoothing filter with the configuration shown in 5 (c), the extracted 3 × 3 pixel information is filtered by this smoothing filter, and smoothing processing is performed on the edge part to create smoothing interpolation data. It is supposed to do. The smoothing filter weights the pixel of interest * as the center because the image may be too blurred by simple uniform smoothing.

The judgment results of the threshold value judgment units 66 and 67 are supplied to the gate 68. The gate 68 controls the selector 69 to allow the output from the delay circuit 65 to pass when the threshold determination unit 67 performs the isolated point determination even if the threshold determination unit 66 performs the edge detection, and When the determination unit 66 detects the edge portion and the threshold determination unit 67 does not perform the isolated point determination, the selector 6
9 to pass the output from the smoothing filtering unit 6465, and further to control the selector 69 to pass the output from the delay circuit 65 when the threshold value determining unit 66 does not detect the edge portion. It has become.

In such a configuration, the 3 × 3 matrix extraction unit 61 extracts information of 3 × 3 pixels centered on the pixel of interest *, and the information is extracted by the edge detection filtering unit 62 and the isolated point detection filtering unit 63. , To the smoothing filtering unit 64 and the delay circuit 65, respectively. The edge detection filtering unit 62 performs edge detection filtering processing, and the threshold determination unit 66 compares the result with the threshold Th1 to determine whether or not the pixel of interest * is an edge portion. In addition, the isolated point detection filtering unit 63
Then, isolated point detection filtering processing is performed, and the threshold value determination unit 67 compares the result with the threshold value Th2 to determine whether or not the pixel of interest * is an isolated point.

When the edge is not detected or when the isolated point is detected even if the edge is detected, the selector 69 selects the delay circuit 65 to select the pixel of interest *.
The value of is passed through as is and output. When the edge detection is performed and the isolated point detection is not performed, the selector 69 selects the smoothing filtering unit 64, and the value of the pixel of interest * is changed to interpolation data by smoothing processing by the smoothing filter and output. To be done.

In this way, the interpolation data is generated only for the edge portions of characters / line drawings, etc. excluding the edge portions of horizontal lines and vertical lines. Further, regarding the filtering process, since the original image data has a compressed bit number after being multi-valued, for example, 3 bits in the embodiment, the calculation itself is very light, and the logic It is also possible to realize with only the configuration.

Further, since the created interpolation value uses the structure of the multi-valued image data for gradation reproduction as it is, the size of the original image data before interpolation and the size of the image data after interpolation are invariant and high. Without adding resolution image data and memory, and without causing a decrease in recording speed,
A sufficient smoothing effect can be obtained.

[0061]

According to the inventions of claims 1 to 9, the edge portion of an image can be smoothly reproduced by utilizing the data structure of a multi-value gradation image without additionally creating special image data. As a result, it is possible to provide an edge interpolation method for an image forming apparatus that can obtain a sufficient smoothing effect without using high-resolution image data and without causing a decrease in recording speed.

According to the tenth and eleventh aspects of the invention, the edge portion of the image can be smoothly reproduced by utilizing the data structure of the multi-value gradation image without additionally creating special image data. As a result, it is possible to provide an edge interpolating device for an image forming apparatus that can obtain a sufficient smoothing effect without using high-resolution image data and without lowering the recording speed.

[Brief description of drawings]

FIG. 1 is a perspective view of a main part showing a first embodiment of the present invention.

FIG. 2 is a block diagram showing a hardware configuration of the same embodiment.

FIG. 3 is a block diagram showing a configuration of an image processing unit of the printer controller according to the embodiment.

FIG. 4 is a block diagram showing a configuration of a printer engine according to the embodiment.

FIG. 5 is a diagram showing a pixel size of each gradation in the same embodiment.

FIG. 6 is a diagram showing a configuration of a 3 × 3 pattern matrix.

FIG. 7 is a diagram showing an example of pattern matching in which minute pixels are added to a target pixel.

FIG. 8 is a diagram showing an example of pattern matching in which a target pixel is minutely deleted.

FIG. 9 is a diagram for explaining a method of obtaining an interpolation value in the same embodiment.

FIG. 10 is a diagram showing an example of interpolation by smoothing according to the same embodiment.

FIG. 11 is a graph showing the relationship between ink ejection volume and ejection speed.

FIG. 12 is a diagram for explaining a relationship between an ink ejection speed and a dot print position on a recording paper.

FIG. 13 is a diagram for explaining interpolation by smoothing according to the same embodiment.

FIG. 14 is a principal block diagram showing a second embodiment of the present invention.

FIG. 15 is a view showing a configuration of various filters used in the same embodiment.

[Explanation of symbols]

1 ... Recording medium 3, 4, 5, 6 ... Line inkjet head 24 ... Smoothing processing section

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI H04N 1/409 H04N 1/40 101D (58) Fields surveyed (Int.Cl. ⁷ , DB name) B41J 2/01 B41J 2 / 205 B41J 2/21 B41J 2/485 B41J 2/52 H04N 1/409

Claims (4)

(57) [Claims] 1. A printhead in which a plurality of print elements are arranged in a line is provided, and a size of a print dot by each print element of the printhead is changed to form a multi-gradation two-dimensional image on a print medium. An edge interpolation method for an image forming apparatus, characterized in that, in the image forming apparatus to be formed, edge interpolation is performed using recording dots of different sizes for gradation reproduction excluding minute size recording dots for low gradation. 2. An ink jet head having a plurality of ink ejection openings arranged in a line is provided, and the size of a recording dot is changed by changing the amount of ink droplets ejected from each ink ejection opening of the ink jet head. In an image forming apparatus that forms a multi-gradation two-dimensional image on a recording medium that moves in a direction orthogonal to the direction in which the ink ejection ports of an inkjet head are arranged, recording dots of different sizes for gradation reproduction are used. The image is characterized in that the size of a recording dot that interpolates an edge by performing the edge interpolation and interpolates the rear edge in the sub-scanning direction in which the recording medium moves is larger than the size of the recording dot obtained by the pattern matching process. Edge interpolation method of forming apparatus. 3. A recording head in which a plurality of recording elements are arranged in a line is provided, and a size of a recording dot by each recording element of the recording head is changed to form a multi-gradation two-dimensional image on a recording medium. In an image forming apparatus for forming, an edge determination means for determining whether or not a target pixel is an edge portion by using an edge detection filter, and whether or not the target pixel is an isolated point by using an isolated point detection filter And an interpolated multi-valued data generation means for generating multi-valued data for edge interpolation with respect to a pixel of interest using a smoothing filter, and the edge judgment means performs edge part judgment. And a selector for outputting the multivalued data for edge interpolation generated by the multivalued data generation means for interpolation when the isolated point determination means makes a non-isolated point determination as the data of the pixel of interest. Edge interpolator of the image forming apparatus characterized by a. 4. The edge interpolating device for an image forming apparatus according to claim 3, wherein a filter for detecting an edge only in an oblique direction is used as the edge detecting filter.